A known solution for carrying out a measurement of the angular position of a rotating element is by equipping said rotating element with a toothed wheel with a detector, disposed facing it on a fixed structure, designed to detect the presence or the absence of a tooth. Such a detector, when the rotating element and hence the toothed wheel rotate, allows a crenelated signal c of the type shown, as a function of the time t, on the diagram 2 in FIG. 1B to be obtained. Such a signal c can be processed by integration or by counting of the teeth in order to obtain a signal a of the type shown, as a function of the time t, on the diagram 3 in FIG. 1C, which is indicative of the angular position α of said rotating element.
Such a sensor is conventionally used in the field of the control of internal combustion engines, with a toothed wheel typically comprising 60-2 teeth (60 teeth with an equal angular distribution and two contiguous missing teeth so as to form an index). Such a toothed wheel driven by the crankshaft provides a precise measurement of the angular position of the engine within its cycle.
A precise reference comprising a measurement of the angular position and a measurement of the time at the moment of said measurement of angular position allows the mechanical movement to be synchronized with the engine control means in order to accurately control events such as the ignition.
Time is conventionally measured by means of a clock producing a linear signal T of the type shown, as a function of time t, on the diagram 1 in FIG. 1A.
In order to provide a precise reference for angular position, at a chosen given moment in time, a simultaneous measurement of time and a measurement of the angular position must be available.
Obtaining such a measurement, which could then be used by a processing unit, may be carried out in several known ways.
According to a first way, a hardware acquisition device is employed to carry out such an acquisition, which is referred to as a hardware acquisition. Such a hardware acquisition device advantageously allows a deterministic and fast acquisition and hence a good precision on the time of acquisition. The simultaneous acquisition of two measurements, time and angular position, requires two such devices. However, such a hardware device is costly and it is natural to want to limit their number.
According to a second way, referred to as software acquisition, a software acquisition device, for example that forming the processing unit executing the method or else that executing the engine control program, is employed to carry out such an acquisition. Such a manner of acquisition does not increase the cost, in that it uses a pre-existing software device. However, as illustrated in FIG. 1D, such a software device suffers from a non-deterministic and long latency time or delay 5. Thus, a software acquisition triggered at the time t1 only carries out an acquisition of the angular position at the time t2, thus causing a corresponding measurement error Δα detrimental to operation as shown on the FIG. 1C.
Other high-performance software devices exist allowing a software acquisition to be carried out with performance characteristics comparable to those of a hardware device. However, such devices are very expensive and, consequently, excluded from the solutions to be envisioned for reasons of cost.